Electric heating unit



Feb. 12, 1952 D. B. cox

ELECTRIC HEATING UNIT Filed March 15, 1949 VENTOR. Jaucan j. [bx

I I. II I I l N Fl TTOIP/VEYS Patented Feb. 12, 1 952 OFFICE ELECTRICHEATING UNIT Duncan B. Cox, Woodbury, N. Y.

Application March 15, 1949, Serial No. 81,550

1 Claim.

This invention relates to an improved electric heater in elongated stripor ribbon form.

It is an object of this invention to provide an improved heater of theabove character which is simple and inexpensive to manufacture, which issaf and efficient in operation and which is relatively rugged so as towithstand reasonable wear and tear.

A further object is the provision of an electric heater in the form of apro-formed continuous ribbon having a plurality of separate conductorstherein and which can be cut to any desired length and the conductorsthereafter joined together to form the desired circuits.

My heater has many different purposes and uses. However, it isparticularly useful in association with water pipes to prevent thefreezing thereof. Heretofore, it has been proposed to insulate suchpipes to prevent their freezing. However, this is not very satisfactorysinc the insulation does not prevent the water from freezing when it isstationary or static within the pipe for any protracted period of time.It has also been proposed to use an electric heater consisting of asingle strand of Nichroine Wire wrapped in a layer of asbestos andcovered with several layers of varnished cambric plus a coating of lead.Th two ends of a suitable length, say 60 feet, are connected to theblades of a conventional attachment plug for connection to a currentsource. Such heaters, however, are relatively expensive and dillicult toinstall because of the stiffness and weight of the cable. They arerelatively inefficient because of the small area of contact between theround cable and the pipe. In some instances it has also been proposed touse a strand of resistance wire coated with a plastic material. Indevices of this type the two ends of a suitable length are also tion,which will provide maximum heat transfer from the unit to the pipe towhich it is applied, which is so designed and constructed as to providemaximum heat dissipation in the air to prevent undue elevation of thetemperature thereof, which is constructed so as to be flexible in designso that the electrical circuits may be readily arranged to meetparticular operating conditions and which is sufliciently rugged to beable to withstand the reasonable use and abuse to which a heater of thistype is subj ected.

In the accompanying drawing- Fig. 1 is a side elevation of a water pipewith one of my heaters in association therewith;

Fig. 2 is a fragmentary partially sectional view of one of the heaterunits;

Fig. 3 is a fragmentary view of the ribbon material from which theheater is made;

Fig. 4 is a transverse sectional view on the lines '4-4 of Fig. 2;

Fig. 5 is a schematic view showing the circuit involved in a heater ofthe type illustrated in Fig. 2; and

Fig. 6 is a schematic view of a slightly modified form of circuit.

My improved heater consists generally of an elongated ribbon or stripllformed of a plurality of conductors H embedded in a plastic body It]and having a cap l2 encasing the return connections of the conductors atone end and a plug [3 at the opposite end.

The plug I3 is of conventional construction being formed of a body ofinsulating material with to the opposite end of the ribbon 9. The bodypor tion It] is made of a flexible thermoplastic material which canwithstand reasonably high temperatures and having high dielectriccharacteristics and for thispurpose I prefer to use a vinyl resinparticularly a plasticized polyvinyl chloride. As shown the conductorsare embedded in the plastic medium of the body which serves not only asan insulator but also as a structural member to properly position andsupport the conductors relative to each other.

As shown most clearly in Fig. 4 the body of the ribbon is of corrugatedor ribbed construction with the corrugations or ribs runninglongitudinally. The corrugations are in the form of tubular orcylindrical portions 15 surrounding the conductors and connectedtogether by flat web-like portions I6. The corrugated constructionserves to augment heat radiation or dissipation so as to prevent undueincrease in the temperatur of the unit or of portions of theunit not incontact with a water pipe or other article. At the same time thecorrugations do not detract from the heat transfer efficiency of thedevice when it is applied to a water pipe.

The conductors I l are made of a high resistance alloy such as Nichromeor stainless steel. A plurality of separate conductors of this type areembedded in the plastic medium of the ribbon in spaced relationship asshown and for the purposes indicated herein I have found that optimumresults are obtained by employing four such conductors. Thus, where itis desired to use my heater in association with water pipes to preventfreezing it is desirable to have a heat dissipation in the order of '7or 8 watts per foot. An even number of wires must be used to completethe circuit at the same end of the ribbon. In order to obtain thedesired heat dissipation with the voltage of 110-120 volts generallyavailable in household electric circuits in a ribbon of reasonablelength I have found that four conductors should be employed. If twowires are employed each wire would have to dissipate 3 to 4 watts perfoot. My tests show that this results in too high a temperatur for theplastic insulation to give good service over a period of years. Also,the ribbon would be of excessive length or the wires would have to be sofine that they would have insufiicient tensile strength. If, on theother hand, 6 or 8 wires are employed the cost is increased without anyworthwhile advantage.

The members 2 l in addition to being the electric conductors are thetensile members supplying the principal tensile strength. Although theplastic has considerable tensile strength in itself, my tests have shownthat it has such a low modulus of elasticity as compared to that of anymetal which might be used for the conductor, that before it had beenstretched sufficiently to carry an appreciable part of any appliedstress, the conductor will be permanently stretched, if not broken.Hence, I have found that the design must provide for a conductorsufficiently large in diameter to carry any applied stress by itself,without appreciably stressing the plastic. Where a chrome nickel steelof the type indicated is used in the conductors, I have found thatsatisfactory results are obtained by using annealed wire with a diameterof approximately .020". This rovides a tensile strength of approximately30-pounds for each conductor. If hard wire is used greater strengthwould be obtained but the finished tape is springy and more difhoult toinstall because it tends to spring away from the pipe at bends insteadof readily conforming. If the ribbon does not have the desired tensilestrength it might be subject to stretching at localized areas with theresult that the conductors in those areas will be drawn more finely andthe resistance increased. This, of course, results in a proportionatelocal increase in heat dissipation and is extremely objectionable,because of the reduced life for the plastic which would result. In orderto avoid this possibility of stretching I have found that a wire sizesmaller than .0159 cannot successfully be used. Stainless steel wire of.0159 has a tensile strength of approximately 19 pounds which issatisfactory in the complete ribbon.

The spacing between the conductors II should be such as to permitadequate heat dissipation and so as not to create any localized areashaving excessive temperatures which will cause the plastic material todeteriorate. Thus, for conductors of the type referred to above, used inconnection with ordinary household current I have found that bestresults are obtained by spacing the conductors between 1 5" and apartwith an optimum spacing of .120" from the standpoint of both cost andefficiency. Wider spacings increase the cost without making a worthwhiledecrease in the maximum temperature, and smaller spacing do not offersuflicient cost saving to offset the disadvantage of increasedtemperature between the wires.

In using my device I have found that it is desirable that it be soconstructed that it can be readily bent to conform in shape with thepipe or other article to which it is applied. The plastic body portionis flexible and permits the ribbon to be bent. I prefer to form theconductors II from annealed wire which not only can be readily bent butalso will remain in the new shape or position after it has been so bent.

Economy in production and flexibility of design are obtained by makingthe ribbon 9 in long continuous lengths as shown in Fig. 3. The ribboncan then be cut to the desired lengths, the circuit between theconductors completed in the desired manner, and the insulating cap l2applied to one end and the plug 13 to the other end of the cut sectionof the ribbon.

In Figs. 2 and 5 I have illustrated the circuit connection for a ribbonof shorter length. Thus, it will be seen that the two adjacentconductors on both sides of the ribbon are twisted together and solderedat the capped end as shown at H and I8 and the two central conductorsare connected together and soldered at the plug end of the ribbon asshown at l9. This provides a continuous circuit from one of the prongs Mof the plug lengthwise of the ribbon four times and terminating at theother prong I4 of the plug. I have found that when connected in thecircuit illustrated in Figs. 2' and 5 and used with ordinary householdcurrent a ribbon heater of the type illustrated and described above andapproximately 20 in length will provide heat dissipation ofapproximately '7 or 8 watts per foot.

In Fig. 6 I have illustrated the circuit to give the same heatdissipation for a ribbon of double the length made from the same ribbon.Accord ing to this circuit the two adjacent conductors l l on both sidesof the ribbon are connected in parallel to the respective prongs M ofthe plug 13 as shown at 20 and 2|. At the opposite or capped end of theribbon all of the conductors are connected together as shown at 22. Ihecircuit of Fig. 6 provides one pass in each direction for the length ofthe ribbon, each pass extending through a pair of parallel conductors.When a device of this type illustrated in Fig. 6 is connected toordinary household current, a heat dissipation of approximately 7 or 8watts per foot is obtained where the ribbon is approximately 40 ft. inlength.

In Fig. 1, I have illustrated my device as employed in association witha water pipe to prevent the freezing thereof. Thus, the ribbon 9 hasbeen secured with one of its broad surfaces in contact with a water pipe23 and the plug (3 has been engaged in a receptacle or outlet 24. Theribbon may be secured in place in any desired manner as by being tapedor tied at spaced intervals as indicated at 25. When used in the mannerillustrated my device will operate in an eflicient manner to transferheat to the pipe and its contents and prevent freezing thereof. Due tothe construction of my device it will readily conform to anyconfigurations of the pipe such as elbows, traps, return bends or thelike.

It will thus be seen that I have provided an improved electric heater inribbon or strip form which is simple and inexpensive in construction,which is easy to use and operate, which is efiicient in operation andwill provide for uniform heat transfer throughout its length and whichis sufficiently rugged in construction to withstand reasonable use andabuse. Modifications may be made in the illustrated embodiment of theinvention without departing from the invention as set forth in theaccompanying claim.

I claim:

An electrical heater unit comprising: an elongated ribbon of vinylchloride formed with longitudinal corrugations presenting four ribs andthree grooves in alternate relationship, said ribbon being ofsubstantially greater Width than thickness; four elongated attenuatedconductors made of resistance wire at least .0159 in diameter inannealed form embedded. in said ribbon in spaced parallel relationshipwith the conductors in alignment with the ribs of the ribbon, the widthof the grooves in the ribbon and of the space between the conductorsbeing betwen 1%,,

and a plug for providing electric connection to a receptacle at one endof said ribbon said conductors being connected together and to said plugso as to provide a complete electric circuit.

DUNCAN B. COX.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,809,714 Mathews June 9, 19311,936,391 Harrower Nov. 21, 1933 2,075,686 Wiegand Mar. 30, 19372,434,798 Feaster Jan. 20, 1948 2,451,839 Lemon Oct. 19, 1948 FOREIGNPATENTS Number Country Date 272,166 Great Britain June 23, 1927 OTHERREFERENCES Modern Plastics, pages 108, 109, August 1946.

